2 files changed, 32 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index f224d4d1c0ed..89bab66558ef 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -4842,6 +4842,36 @@ int drm_format_vert_chroma_subsampling(uint32_t format)
 EXPORT_SYMBOL(drm_format_vert_chroma_subsampling);
 
 /**
+ * drm_rotation_simplify() - Try to simplify the rotation
+ * @rotation: Rotation to be simplified
+ * @supported_rotations: Supported rotations
+ *
+ * Attempt to simplify the rotation to a form that is supported.
+ * Eg. if the hardware supports everything except DRM_REFLECT_X
+ * one could call this function like this:
+ *
+ * drm_rotation_simplify(rotation, BIT(DRM_ROTATE_0) |
+ *                       BIT(DRM_ROTATE_90) | BIT(DRM_ROTATE_180) |
+ *                       BIT(DRM_ROTATE_270) | BIT(DRM_REFLECT_Y));
+ *
+ * to eliminate the DRM_ROTATE_X flag. Depending on what kind of
+ * transforms the hardware supports, this function may not
+ * be able to produce a supported transform, so the caller should
+ * check the result afterwards.
+ */
+unsigned int drm_rotation_simplify(unsigned int rotation,
+                                   unsigned int supported_rotations)
+{
+        if (rotation & ~supported_rotations) {
+                rotation ^= BIT(DRM_REFLECT_X) | BIT(DRM_REFLECT_Y);
+                rotation = (rotation & ~0xf) | BIT((ffs(rotation & 0xf) + 1) % 4);
+        }
+
+        return rotation;
+}
+EXPORT_SYMBOL(drm_rotation_simplify);
+
+/**
  * drm_mode_config_init - initialize DRM mode_configuration structure
  * @dev: DRM device
  *
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index f7b383bcb6b6..08ed55e02762 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -1115,6 +1115,8 @@ extern int drm_format_vert_chroma_subsampling(uint32_t format);
 extern const char *drm_get_format_name(uint32_t format);
 extern struct drm_property *drm_mode_create_rotation_property(struct drm_device *dev,
                                                               unsigned int supported_rotations);
+extern unsigned int drm_rotation_simplify(unsigned int rotation,
+                                          unsigned int supported_rotations);
 
 /* Helpers */